LD50LC50

LD50 and LC50 are standard metrics in toxicology used to express acute toxicity. The LD50, or lethal dose 50 percent, is the amount of a substance required to kill 50% of a defined test population when given by a specified route (such as oral, dermal, or injectable). The LC50, or lethal concentration 50 percent, is the concentration of a substance in air or in a liquid medium that causes the death of 50% of the population after a defined exposure period. LD50 is typically reported in units of mass per body weight (for example mg/kg), while LC50 is reported as concentration in the exposure environment over time (for example mg/L or mg/m3 at a given duration).

Determination of these metrics relies on dose-response experiments in animals or other test systems. Multiple dose levels are tested, and mortality is recorded over a defined observation window, often 24 to 96 hours. Statistical methods, such as probit or logit analysis, are used to estimate the dose or concentration that corresponds to 50% mortality. Routes of exposure and the species tested strongly influence the values; common species include mice, rats, and rabbits, with oral, dermal, and inhalation as typical routes.

In hazard assessment, LD50 and LC50 have historically been used to categorize acute toxicity and compare relative potencies of substances. They are part of regulatory frameworks such as the Globally Harmonized System of Classification and Labelling (GHS). However, they are limited in predicting human risk and chronic effects, and results vary with species, strain, and experimental conditions. Ethical considerations have driven the development of alternative approaches and non-animal testing methods where feasible.